Hello, I am Keith one of the experts on Just Answer, and pleased to be able to help you with your question.
Here is the list from the Gov UK web site of the products upon which you should not be paying VAT:
'Qualifying products or services
Your supplier can tell you, but usually products designed or adapted for a disability qualify. For example, certain types of:
The full advice is available here:
It would appear from the Govt web site that you have to apply for this VAT exemption before you actually order the goods.
So what to do, well I would suggest kick up a fuss both with the supplier, your local trading standards, your MP, local councilor, your local paper, your local radio station and even the national press not to mention Facebook, twitter etc. Big firms like Amazon do not like this sort of adverse publicity, it is not good for their reputation or business. They may try a mealy mouthed approach that you should have advised them initially of your disability viz a viz VAT, but they may crumble in the long term.
So stir the mud unmercifully would be my approach. I myself have been disabled for some 20 years, but the only purchase I have fortunately had to make many years ago was a folding walking stick for air travel and I now ask for a wheel chair at interchanges and destination which by passes all the queues as you are passed through in advance of even aircrew!
Time to do a Victor Meldrew!
I do hope that I have shown you a way forward in your situation.